Yes, it's selfish, but that's not necessarily wrong. It's also reasonable that she had expectations that you would have changed your plans (most hikers will never actually try or finish their hike). Regarding your marriage, most people fail at marriage because they don't accept that change will happen. You must determine if she is able to accept your absence for 6 months, and she must determine if this hike is essential to you. Then you'll need to dance around the issues until there's a resolution. If either of you are unwilling to change then your marriage is probably doomed either way. Perhaps it's for the better, perhaps not. Only you can tell (assuming you're sufficiently aware). I know many that have thrown away a good marriage out of lack of awareness, and plenty that stayed too long in a bad marriage because of same. Best of luck.